Download Undelete and upload via the Plugins > Add New page (or search and install inside WordPress)
Activate the plugin.
Everything else is automatic. When you get overexcited and accidentally delete something important, head over to Tools > Undelete/Restore to get it back.
Leave a comment on the plugin page if you need any help. Let's face it though, if you can tie your shoelaces, you can probably install this plugin. No offence meant to anybody who can't tie their shoelaces... but come on... seriously?
Requires: 3.1 or higher Compatible up to: 3.1.4 Last Updated: 2011-5-2 Downloads: 2,784